Method of producing zinc alloy

ABSTRACT

A METHOD OF PREPARING A ZINC-BASE ALLOY CONTAINING COPPER AND TITANIUM OR COPPER, TITANIUM AND MANGANESE, SUBSTANTIALLY FREE OF IDIOMORPHIC CRYSTALS OF ZINC-TITANIUM INTERMETALLIC COMPOUNDS, IN WHICH A MASTER ALLOY IS FORMED IN MOLTEN FORM IN A FIRST VESSEL AND SAID MASTER ALLOY ADDED TO MOLTEN ZINC IN A SECOND VESSEL OT FORM THE FINAL DESIRED ALLOY COMPOSITION, SAID MASTER ALLOY AND FINAL ALLOY BEING CONTINUOUSLY AGITATED DURING THEIR RESPECTIVE FORMATIONS.

Sept. 26, 1972 R. F. REDDEN 3,594,199

METHOD OF PRODUCING ZINC ALLOY Filed Aug. 17. 1970 s Sheets-Sheet 1 ROBERT E REDDEN BY: QM

Agent R. F. REDDEN METHOD OF PRODUCING ZINC ALLOY 3 Sheets-Sheet 2 INVENTOR ROBERT F. REDDEN FIG. 4

Agent Sept. 26, 1972 F iled Aug. 17, 1970 Sept. 26, 1972 R. F. REDDEN METHOD OF PRODUCING ZINC ALLOY 3 Sheets-Sheet 5 Filed Aug. 17, 1970 FIG. 5

INVENTOR ROBERT F REDDEN a \,%s

Age nt United States Patent Office 3,694,199 Patented Sept. 26, 1972 Int. Cl. czzc 17/00 U.S. Cl. 7s-17s c 1 ,6

ABSTRACT OF THE DISCLOSURE .A method of preparing a zinc-base alloy containing copper and titanium or copper, titanium and manganese,

Cominco Ltd., Montreal, Quebec,

, amount of chromium or chromium plus manganese facilitated rolling and resulted in an improved rolled product.

A method for the preparation of quaternary or quinary zinc alloys containing 0.5-2% copper, 0.03-0.2% magnesium and O.1-0.4% titanium is given in U.S. Pat. No.

. 3,146,098 issued to Saarivirta et al. A melt of zinc and copper, for example, is raised to 500 C. for the addition of magnesium and then to about 750 C. for the addition of titanium sponges. The melt is held at about 750 C. for about 10 to 20 minutes, with periodic agitation if desired,

and then cast into molds. An inert gas cover is used.

substantially free ofidiomorphic crystalsof zinc-titanium alloy being continuously agitated during their respective formations.

BACKGROUND OF THE INVENTION This invention relates to the preparation of zinc base alloys and in particular is directed to a rapid methodof preparing improved zinc base alloys containing copper and titanium or copper, titanium and manganese which are free of large idiomorphic crystals of zinc-titanium intermetallic compounds.

U.S. Pat. 2,319,179 to Daesen discloses a method for the preparation of zinc-copper-titanium alloy containing 2 to 5% Cu and 0.02 to 0.50% Ti. It is taught, that, if copper was added to molten zinc, this copper would act as a dispersant for subsequently added titanium. A superior ternary alloy was obtained by following this alloying procedure if 2% Cu or more was used. Daesen reported that, with 1% Cu or less, it was impossible to disseminate evenly more than about 0.05% Ti and that theresulting alloys had inferior properties.

Other investigations have developed methods for making zinc-copper-titanium alloys containing less than 2% copper. Boyle, in U.S. Pat. No. 2,472,402, discloses preparation of a Zn-4% Ti master alloy by heating zinc and titanium for about 8 hours in a crucible at about 800 C. The master alloy was cast into a'thin slab which was crushed-and alloyed with zinc by melting'and holding the mixture at 550-575 C. for about one hour. Copper was added later as a brass intermcdiate'to form a final alloy crates of high melting point metal, such as titanium or its intermetallic compounds with zinc, Urban et a1. describes in U.S. Pat. 3,254,993 a method in which titanium was dissolved into and alloyed with zinc at a temperature in the range of from about 65 0 C. to 850 C. until the titanium was uniformly dispersed and the resulting alloy rapidly chilled in small individual masses to produce a homogeneous, fine grain size zinc-titanium master alloy containing 0.5 to 5% Ti. Final alloy containing 0.35 to 2% Cu and 0.15 to 0.5% Ti was then prepared by rapid chilling of a substantially uniform dispersion formed by adding master alloy and copper to molten zinc. r v

The formation of zinc and zinc base alloy ingots with improved workability is disclosed in'U.S. Pat. No. 1,777,- 659 to Stay et al. Rapid controlled solidification of melt produces an equiaxed grain structure without large, irregular grains. v Improvement of zinc-copper-titanium alloys by addition of another metal is illustrated by U.S. Pat. No. 3,006,758, issued to Giuliani et al., in which it is stated that a small In recent United States Bureau of Mines studies of zinccopper-titanium alloys, 'Reports of Investigations 6690 (1965), 7089' (1968) and 7229 (1969), alloying was accomplished by use of a brass containing 60% copper and a zinc-titanium alloy containing 3 to 3.5% titanium as master alloys.

Although the foregoing patents disclose zinc base alloys containing copper and titanium, and copper, titanium and manganese, and disclose various techniques for achieving improved physical and chemical properties in said alloys, difliculties have been encountered in achieving rapid production of such zinc base alloys which are consistently free of deleterious idiomorphic crystals of zinc-titanium intermetallic compound. Such crystals adversely affect the working properties of these alloys.

SUMMARY OF THE INVENTION I have discovered surprisingly that by adding copper, then titanium, to molten zinc, with continuous, vigorous mixing to-make a master alloy, and then adding this master alloy, still in molten form, to molten zinc, also with continuous, vigorous mixing, alloys with good working properties for the fabrication of articles having good strength and ductility, dimensional stability, creep resistance and intergranular corrosion resistance can be rapidly obtained. The method of my invention for preparing a zinc-base alloy composition consisting by weight of from about 0.8 to about 1.2% copper, about 0.05 toabout 0.15% titanium, and the balance zinc, in cast form substantially free of idiomorphic crystals of intermetallic compounds, comprises forming and continuously agitating a supply of molten master alloy containing up to about 12% copper, up to about 1.4% titanium and the balance zinc in a first vessel, feeding molten zinc into a secondvessel'and transferring to said second vessel appropriate predetermined amounts of molten master alloy from said first vessel in relation to the flow of molten zinc to said second vessel to form said molten zinc-base alloy composition','coricurrently agitating the molten metal in the second vessel, withdrawing molten alloy composition from said second vessel, and casting said alloy to produce said zincbase alloy composition in cast form.

A master alloy of zinc containing up to 12% manganese can be added to the above alloy composition, in molten form, to produce a zinc base alloy having 0.8 to about 1.2% copper, 0.5 to about 1.5% manganese, 0.05 to about 0.15% titanium, and the balance zinc; said zinc-copper-manganese-titanium alloy being substantially free of idiomorphic crystals of zinc-titanium intermetallic compounds.

It is the principal object of the invention therefore, to form zinc-copper-titanium alloys and zinc-copper-titanirim-manganese alloys that do not contain large idiomorphic crystals of zinc-titanium intermetallic compound.

It is also an object of the invention to provide an improved and rapid method of consistently forming zinc base alloys having desired properties by the application of simple mixing techniques, thereby gaining such benefits as lower operating temperatures, decreased volatilization of zinc and decreased oxidation of titanium.

DESCRIPTION OF EXAMPLES OF THE METHOD can be attained, will become, apparent from the following descripftion of examples of the method of my invention.

' EXAMPLE 1 p p The following example shows that, in the preparation of master alloy with continuous stirring under -a coke cover, complete alloying can be effected'within one half hour. A batch of master alloy with additivesto give 12% Cu and 1.2% Ti wasprepared, with the titanium-being added at 700 C., a convenient temperature -'above the melting point .of thealloy, i.e., about 600 0., and below a temperature at which there is excessive volatilization of zinc and oxidation of titanium. After. the. titanium addition, the temperature was changed as shown: in Table I. Splash sampling of the molten alloy after thetime intervals tabulated indicated that alloying was completed within the first 0.5 hour and that rapid oxidation of "titanium did not occur until the melt temperature wasraised-to TABLE I Composition ofialloy Time after Temperapercent I titanium addition ture t (hours) v I O.) Cu Ti For rapid alloying and for low loss of titanium-{an alloying temperature range of from 700 to 790 C. is indicated for operations in which a coke cover is used.

EXAMPLE II quickly. Rapid-dissolving of titanium occurred. 'Assays were made on splash samples, i.e. samples that had been ladled from the melt and poured into water.

TABLE II.

Composition of splash Tempera- Time after sample, percent T1 added ture range Ti addition Test percent C (minures) Cu Ti 20 0. 002 O. 95 1 1. 4-. 705-755 30 0. 001 0. 90 60 0. 002 0. 80, 20 0. 002 1. 20 2 1. 4 680-715 30 0. 002 1. 25 60 0. 002 1. 20 20 0. 9 1 0. 7,0 3 1. 4 695-730 30 0. 94 1. 25 60 =0. 91 v 1. 20 20 2. 8. 1. 15 4 1. 2 675-705 30 2. 9 1. 10 60 2.9 1. 10 20 5. 1. 15 1. 3 670-705 30 4. 9 '1. 60 4. 8 1 11. 15 6 1. 4 705-695 g g The temperatures shown in Table II were maximum and minimum thermocouple observations that were made during each test. In Test 1, it maybe observed that-the percent titanium in thealloy had fallen off rapidly with time, to about 70% of the added titanium after 20.min-.

utes and to about 60% after 60 minutes. The 755 C. temperature 'that was reached during the test was too high. Excessive oxidation of titanium occurred and fuming of zinc was visible. Test 2 is a repetition with the same composition but with a lower temperature range. With the temperature between 680 and 715 C.,' 85-90% ofthe added titanium remained in the alloy, even. after 60 minutes mixing. The copper in the alloy of Tests 1 and 2 was present as impurity. In Test 3, the low value of titanium" in the 20 minute sample,'i.e. 0.70%, resulted from inadequate mixing. In the remaining samples, satisfactory compositions with respect to titanium were obtained, i.e. losses of titanium by oxidation were within about '10 percent. The observed operating temperatures, ranging from 670 to 730" (3., show that titanium can be alloyed rapidly-with zinc containing.0.00 1 to 12% copper between 670 and '730 without excessive oxidation oftitanium. v

'"In' the prepartion of the allow of Test 6, there was no mixing for the first" 20 minutes. Beginning 10 minutes after "the 60'minute' sampling, the alloy was removed from the melting pot by ladling over a 30 minute period during which stirring was continued. Assays were obtained on samples that were removed'at the start, half way through and at the end of the ladling period. Titanium assays were 1.3%, 1.5% and 1.2% respectively, while copper assays were 11.7%, 11.8% and 11.7%. There was no extensive oxidation of the titanium during this time. Prior to the above. observations, it would appear that, with vigorous mixing, maintenance of a conventional protective cover, either as an inert gas oras a floatingreductant, would be difiicult. In the above tests, vigorous agitation dispersed the titanium rapidly at temperatures that were generally lower than the temperatures of prior art processes. Because of decreased time and temperature, less oxidation of. titanium occurred and no floating reductant orfinert gas cover was required. The tests dem- Qnstrate ability to prepare master alloy within 20 minutes of titanium addition and ability'to hold unprotected master falloy for at least 60 .minutes between 67.0" C. to 730? C. "without excessive oxidation of titanium.

EXAMPLE III- In a like'ma'nner, a molten quaternary zinc alloy. containing 10.1%.Cu, 8.7% Mn and 0.95% Ti was prepared byaddin'g manganese and titanium chips simultaneously to the, vortex of continuously mixing zinc-copper, alloy at 680?, C. Sampling after 45 minutes, 2 hours, 4 hours and 5 hours of continuous mixing between 680 and 710 C. showed thatalloying was completed within 45 minutes andthatno'signilicant change in COIIIPOSitiOHJOdCHITCd within 5. hours. No protective cover was used. I

Preparation of the final .alloy composition was adapted to a partially automated system in which zinc from a melting furnace was caused to flow throughand tobe stirred with. predetermined amounts ofmaster alloyin anopen-top mixing vesseL Rate of continuous flow of zinc through the vessel was controlled by-the rate of removal of mixed alloy. In order to obtain the desired composition of final alloy, definite volumes-of molten master alloy as measured with a dipper were poured into the; mixing vessel at spaced intervals of time so that its rate of input was synchronized-with that of themolten zinc.

Synchronized mixing of readily miscible solid additive oxidation of the easily oxidized metal.

- EXAMPLE IV The application of the process for the production of a specific zinc-copper-titanium alloy will now be discussed in detail. An open-top refractory melting vessel was gas fired to melt 1325 pounds of special high grade zinc to which 180 pounds of copper, 99.99% Cu, were added. The temperature was raised to 680-700 C. The copper dissolved within 30 minutes. A top-mounted graphite stirrer with a barrel-type impeller todrive the melt to the bottom of the vessel was introduced and was operated to effect vortex mixing. Nineteen pounds of titanium sponge, about one-quarter inch particles in size, containing 99+% Ti, were added to the vortex and dissolved within 20 minutes. Oxidation of the titanium was not excessive. No protective cover was required. Stirring of the master alloy, at about 700 C., was continued during the removal of volumetrically measured portions. This stirring prevented loss of titanium by excessiveoxidation resulting from localized overheating. This molten master alloy contained about 12% copper and 1.2% titanium.

Preparation of final alloy was carried out in' a heated, open-top, cylindrical vessel that was equipped to receive a continuous flow of molten zinc on one side and to discharge mixed alloy by means of a launder on the opposite side.

A graphite stirrer with a barrel-type impeller to drive molten metal to the bottom of the vessel was introduced and was operated to efiect vortex mixing. After proportionate addition of molten zinc and master alloy to fill the vessel, with the stirrer operating, intermittent additions of master alloy were synchronized with a continuous flow of molten zinc through the vessel, i.e. a 23.9 cu. in. dipper full or 5.4 pounds of master alloy was added to the vortex for each 56 pounds of final alloy that was withdrawn to be cast into a billet. A 1524 pound batch of master alloy was used within one hour of the addition of the titanium to the zinc-copper melt to produce 14,300 pounds of final alloy in 255 billets with an average analysis of 1.14% Cu and 0.14% Ti. 7

Analyses in Table III show uniformity of distribution of copper and titanium in successively cast billets of final alloy.

TABLE III Percent Percent Percent Percent -Blllet No. On Ti Billet No. u Ti EXAMPLE V In another example, in which a smaller proportion of master alloy was used, final alloy flowing from the mixing vessel had the following assays.

Although adequate mixing of the final alloy was obtained with the apparatus described, short circuiting, i.e., direct flow of unalloyed molten zinc from the inlet to the outlet launder, may be prevented by use of a two chamber mixing vessel. A central, vertical baffle between the chambers causes the metal to flow downward in the first chamber, to which all additions are made, through a communicating passage at the bottom, and upward in the second chamber to the overflow launder. Each chamber is equipped with a stirrer which forms a vortex and which drives the melt downward. Flow through the vessel is by gravity.

Molten final alloy may be cast into conventional billets as described above or it may be fed to a continuous castingmachine where billets for subsequent extrusion or forging are made directly. In the latter case, the occurrence of smaller grain size resulting from more rapid cooling may be expected. Remelting of conventional billets and recasting in a form suitable for forging did not promote growth of idiomorphic crystals of intermetallic compound and therefore did not adversely affect the working properties of the alloy.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a photomicrograph at magnification of x of an ingot conventionally cast from an alloy prepared according to the method of my invention;

FIG. 2 is a photomicrograph at magnification of 800x of the ingot shown in FIG. 1;

FIG. 3 is a photomicrograph at magnification of 800x of a billet continuously cast from an alloy prepared according to the method of my invention;

FIG. 4 is a photomicrograph at magnification of 800x of the billet shown in FIG. 3; and

FIG. 5 is a photomicrograph at magnification of 100x of a billet continuously cast from zinc-copper-manganesetitanium alloy prepared according to the method of my invention.

FIGS. 1 and 2 are photomicrographs at magnifications of 100x and 800x respectively, of an ingot which con tained 1.02% Cu and 0.09% Ti, conventionally cast in an open-top mold, sprayed with water to set the shell, and then removed from the mold and air cooled. Metallographic examinations of sections of ingots so produced,

of which FIGS. 1 and 2 are representative, show almost equiaxed primary grains of zinc, approximately 100 microns in diameter, surrounded by a eutectic of TiZn and zinc.

FIGS. 3 and 4 are photomicrographs of a continuously cast billet that was formed from a molten alloy which contained 0.99% Cu and 0.09% Ti obtained by the melting of conventionally cast alloy produced according to the method of my invention. They exhibit a much finer structure with the width of the primary grains being apapproximately 8-10 microns and about one tenth their length. Although the continuously cast structure differs somewhat from the conventionally cast structure, both are'alike in their lack of any large crystals of intermetallic compound. Absence of large crystals was also observed in conventionally cast zinc alloy containing 1.07% Cu and 0.13% Ti. This absence of idiomorphic crystals of zinc-titanium intermetallic compound in cast alloy is an important feature of the process of the invention.

Although the description of the method of my invention in connection with the preparation of a zinc-coppermanganese-titanium alloy related to the simultaneous addition of manganese and titanium chips to a zinc-copper alloy, I have found that zinc-copper-manganese-titanium alloys having the desired properties can be prepared by the production of a zinc-copper-titanium alloy having a final composition as has been described and adding thereto a master alloy of zinc containing up to 12% by weight manganese. The final zinc-copper-manganese-titanium alloy has a composition by weight of 0.8 to 1.2% copper, 0.5 to about 1.5% manganese, 0.05 to about 0.15% titanium, and the balance zinc.

This alloy may contain idiomorphic zinc-manganese crystals as shown in FIG. 5. Although zinc-titanium crystals, which have a sharp, angular structure,caus'e stresses that decrease the strength of the alloy, zinc-manganese crystals do not cause stress problems.

This alloy may contain idiomorphic zinc-manganese crystals as shown in FIG. 5. Although zinc-titanium crystals which have. a sharp, angular structure, cause stresses that decrease the strength of the alloy, zinc-manganese crystals have edges that tend to be rounded; These zinc-manganese crystals do not cause stress problems.

By the process of the present invention zinc-coppertitanium alloy containing 0.8 to 1.2% copper and 0.05 to 0.15% titanium was prepared and cast to form billets that were essentially free of idiomorphic crystals of TiZn intermetallic compound. Prevention of the growth of large particles of intermetallic compound was the result of specific features of the alloying process. With prior addition of copper, it was not necessary to hold titanium-containing melt at an elevated temperature for the time required to disperse the copper. With addition of the titanium sponge to rapidly mixing molten alloy of zinc and copper, theere was rapid dispersion of titanium atoms as they separated from the sponge granules and coating of the sponge with intermetallic compound did not occur. The molten master alloy was stirred continuously at a temperature above that at which peritectic solid phases form until it had been added in successive portions to the zinc. Stepwise additions of the master alloy and continuously flowing zinc to rapidly mixing melt resulted in rapid blending and almost instantaneous passage of the composition through the zones in which peritectic phases can be formed. The intermetallic compound does not segregate from molten alloy containing less than about 0.2% titanium. Further, completion of the alloying before excessive oxidation of titanium could occur eliminated the need of a protective cover of reductant or inert gas, which would have been difficult to maintain under the operation conditions. I have found that these steps suppressed the growth of large particles of zinc-titanium intermetallic compound, whose presence in zinc-coppertitanium alloys imparts inferior properties to fabricated products. The process of the invention is also applicable to quaternary zinc base alloys, as shown by the ease of preparation of zinc-copper-manganese-titanium master alloys and the absence of large particles of zinc-titanium intermetallic compound in final alloys.

Cast alloys prepared by my process can be extruded and forged without difiiculty. Fabricated articles have good strength and ductility, are dimensionally stable and creep resistant, and resist intergranular corrosion.

I clami:

1. A method of preparing a zinc-base alloy composition consisting by weight of from about 0.8 to about 1.2% copper, about 0.05 to about 0.15 titanium, and the balance essentially zinc, in cast form substantially free of idiomorphic crystals of zinc-titanium intermetallic.

compounds, which comprises: forming and continuously vigorously agitating a supply of molten master alloy consecond vessel and transferring to said second vessel appropriate; predetermined amounts of molten master alloy from first vessel in relation to the flow of molten zinc to said second vessel to form said zinc-base alloy composion,concurrently agitating the molten metal in the second vessel, withdrawing molten alloy composition from said second vessel, and casting said alloy to produce zincbase alloy composition in cast form. 7

.2. A method as claimed in claim 1, forming the master alloy by dissolving said copper in molten zinc at a temperatureabout 680? to 700 C. and subsequently dispersing said' titanium in granular form in the zinc-copper alloy at a temperature about 670. C. to 730 C.

3. A method as claimed in claim 1, maintaining the molten master alloy temperature between about 670 and 730 C. during transfer of the master alloy to the second vessel. g h

4. A method asclaimedin claim 2 in which. master alloy is prepared by the simultaneous addition of titanium and manganese, said manganese comprising up to 12% 5. A method as claimed in claim 1, in which a master alloy of zinc containing up to 12% by weight manganese is added to the molten zinc-base alloy composition to form an alloy composition consisting of from about 0.8

to about 1.2% copper, about 0.5 to 1.5% manganese, 0.05 to 0.15% titanium, and the balance essentially zinc.

6. A method as claimed in claim 1, vigorously agitating the supply of molten master alloy by vortex stirring.

References Cited I UNITED STATES PATENTS 3,552,951 1/1971 Schelleng -135 X 2,472,402. 6/1949 Boyle 75-178 R 3,113,053 12/1963 Zvanut 75-178 C 3,254,993 6/1966 Urban et al. 75-178 R 2,317,179 4/1943 Daesen 75-178 C 2,428,959 10/1947 Boyle et al. 75-178 R 3,006,758 10/1961 Giuliani et a1, 75-178 R 3,527,601 9/1970 Foerster 75-178 C 3,592,636 7/ 1971 Pohlman et al. 75-178 C FOREIGN PATENTS 1,138,553 10/1962 Germany 75-178 C L. DEWAYNE RUTLEDGE, Primary Examiner E. L..WEISE, Assistant Examiner H j 

